In present power installations, a user installation is typically combines with an uninterruptible power supply (UPS) system, which is provided by a UPS manufacturer. In particular, retrofit applications of UPS systems to existing user installation can be required.
The user installation typically comprises a load, which has to be supplied with power. The load can be a single load or multiple individual loads, which can be considered as a single load from a system point of view. The load can be any kind of AC or DC load, or even a combination thereof. The user installation further comprises at least one AC power source, which is a primary power supply for powering the load. One or multiple AC power sources together form the primary power supply. The user installation still further comprises at least one secondary power supply, which provides power in case of a failure of the primary power supply. The user installation also comprises at least one controllable hardware component, e.g. switches or other components. A system Protective Earth is provided as a common Protective Earth for all components including the power sources and the load.
The uninterruptible power supply system comprises at least one uninterruptible power supply module, and a control device for controlling the uninterruptible power supply system based on at least one system parameter of the uninterruptible power supply system. Hence, the control device receives e.g. measured internal voltages and/or currents of the UPS system for powering the load from the primary and/or secondary power supply.
Static UPS systems, also referred to as solid state UPS systems, refer to UPS systems essentially without movable parts in its power path, in particular without a generator to provide power in case of a failure of the AC power source. Solid state UPS systems include architectures such as dual conversion or off-line, also known as single conversion.
Dual conversion is a very common design for static UPS, e.g. used in data centers. The UPS system comprises an AC/DC converter, also referred to as rectifier, which is provided at its power supply side and connected to the AC power source, a load side DC/AC converter, also referred to as inverter, which is connected to the load, and a DC/DC converter, also referred to as battery converter, which is typically connected to a battery as secondary power supply. The AC/DC converter, the DC/AC converter, and the DC/DC converter are connected to each other by a DC link. In normal operation, AC power from the AC power source is provided through the AC/DC converter and the DC/AC converter to the load. In case of a failure of the AC power source, the load is powered from the secondary power supply via the DC/DC converter and the DC/AC converter.
In single conversion UPS design, the load is directly connected to the AC power source via a power line. A DC/AC converter is typically connected between the power line and a battery as secondary power supply. Power is provided from the secondary power supply via the DC/AC converter in case of failure of the AC power source.
UPS control requirements and consequent built-in control capability usually support the minimum requirements of the basic installation type, based on a severe competition in the market setting stringent requirements on the cost of a standard high volume unit. Some excess capability is usually built in for minor flexibility, but this is not sufficient to support a major variability in system installation.
In this area, the power installation can be challenged by different installation types and/or national legal requirements depending on the place of the power installation.
Power installations typically conform to a few overall classes, TN-(C)-S and IT being the most common. AC power sources may include or be without neutral (N).
Installations that may be termed ‘industrial’, ‘offshore’ or ‘marine’ pose challenges to control of the UPS system. The installations typically have multiple additional transformers and controls/switch gears installed in no standard configuration. This requires additional, application specific sense capability for voltage/current and control capability to operate disconnect and other devices.
Some of the sense and control requirements will be crossing an isolation boundary (e.g. transformer primary and secondary sides) so require special consideration. The isolation requirements may be very severe, as an example a standard UPS is generally dimensioned for Overvoltage Category II (line transient level to expect) but an installation with heavy additional equipment may expect transients up to Category III or even IV.
Additional criteria may apply and a level of local or distributed decision making capability may be preferred or required.
Overall system reliability may require redundancy for critical functions, this may include measurement and communication.
All data has to be available on a relevant magnitude and time resolution for overall system control, usually but not always residing in the UPS system.